Our overall objectives in this project are to define the local immune defences against urinary tract infections (UTI)as they are manifested by urinary immunoglobulin excretion and in vitro assays of antibacterial activity. Past work has shown a unique elevation in secretory IgA excretion following UTI in children with and without identifiable anatomic abnormalities. Also, children with cystitis cystica have been shown to have elevated urinary secretory IgA but not IgG. Current work consists of immunoglobulin quantitation in children with recurrent urinary tracer infection, the running of in vitro antibacterial assays on the urine in conjunction with measurements of urinary pH, osmolality, and urea, and correlation of all these with the patient's clinical course. In addition, we hope to see which urnary immunoglobulin is primarily responsible for any in vitro antibacterial activity that we can document. Use of induced infections in the rat seeks to determine whether coating of bladder bacteria by secretory IgA prevents bacterial adherence to apithelial cells and thus limits bacterial colonization.